class MyClass {

}
var x = new MyClass()
console.log(x instanceof MyClass); // true
console.log(MyClass[Symbol.hasInstance](x));//true


console.log(MyClass)
console.dir(MyClass)
console.log(MyClass[Symbol.hasInstance], typeof MyClass[Symbol.hasInstance])
console.log(Object.getOwnPropertyDescriptor(MyClass, Symbol.hasInstance))
